The invention concerns a method for the automatic control of an internal combustion engine-generator unit.
An internal combustion engine provided as a generator drive is usually operated in a closed-loop speed control system. The actual speed of the crankshaft is determined as the controlled value. It is compared with a reference input, i.e., a set speed. The resulting control deviation is converted by a speed controller to the correcting variable, e.g., a set injection quantity. To stabilize the closed-loop speed control system, a one-revolution or two-revolution filter is provided in the feedback path.
An internal combustion engine of this type is operated in a steady state, i.e., at a constant rated speed. For example, a rated speed of 1,500 rpm corresponds to a power frequency of 50 Hz in a generator application. Due to external influences, a dynamic operating state can arise, for example, in the case of a load rejection. Applicable industrial standards (DIN, VDE) define acceptable speed increases in the event that a dynamic operating state develops, for example, 10% of the rated speed.
DE 199 37 139 C1 describes a method for the automatic control of an internal combustion engine-generator unit, in which the injection start is shifted towards late when a significant load reduction on the power takeoff is detected. A speed limitation curve for limiting the set injection quantity is provided in the injection start input-output map as an additional measure. However, the speed limitation curve restricts the adjustment range in steady-state operation.
DE 103 02 263 B3 describes a method in which the set injection quantity in steady-state operation is limited by means of a first speed limitation curve. This does not take effect until the actual speeds are significantly higher than the rated speed. Consequently, this provides the operator a large adjustment range of the set speed in the steady state. When a dynamic operating state is detected, a changeover is made to a second speed limitation curve, by which the set injection quantity and thus the actual speed are limited.
A generator installation often comprises several internal combustion engine-generator units operating in parallel. A closed-loop load equalization control system ensures that different internal combustion engines produce identical outputs. A higher output is adjusted by the operator by increasing a speed set value. The closed-loop load equalization control system consists in initially allowing an increased set injection quantity on the basis of the higher speed set value and the higher control deviation. A speed controller with an increased set injection quantity as the correcting variable also has a higher integral component. The integral component is converted to a correction speed. A P-degree that can be preset by the operator is critical for this conversion. The correction speed and the speed set value are then used to compute an effective set speed, which, together with the actual speed, is critical for the closed-loop speed control. Since the correction speed is reduced with a rising integral component, the effective set speed falls back to the rated speed, while the set injection quantity remains at the higher level. A higher set injection quantity causes a higher power output of the internal combustion engine.
When the prior-art methods are used, the following problem arises in practice in conjunction with closed-loop load equalization control:
During a load rejection, the actual speed rises very fast. As a result of this, the set injection quantity is reduced by the speed controller. An especially strong reduction of the set injection quantity and the integral-action component occurs when these are limited by the speed limitation curve. An increasing correction speed is computed by the closed-loop load equalization control system due to the falling integral-action component. At a constant speed set value, a higher correction speed means a higher effective set speed. A higher effective set speed causes a smaller speed control deviation. The effect of this is that the limitation of the set injection quantity by the speed limitation curve is deactivated again. Therefore, in the case of a load rejection, the actual speed of the internal combustion engine can overshoot by an unacceptably large amount. Therefore, the prior-art methods are of limited usefulness in a generator installation with closed-loop load equalization control.